Pulses of Fast Electrons as a Tool To Synthesize Poly(acrylic acid) Nanogels. Intramolecular Cross-Linking of Linear Polymer Chains in Additive-Free Aqueous Solution

Abstract

Nanogels of poly(acrylic acid) have been synthesized using a new method, based on intramolecular cross-linking of linear macromolecules in aqueous solution, induced by short (a few microseconds) pulses of fast electrons. Simultaneous generation of a number of carbon-centered radicals along the polymer chain results in predominantly intramolecular recombination, with only a minor contribution of intermolecular cross-link formation and chain scission. This new method allows the synthesis of nanogels in a pure system consisting only of polymer and water, in the absence of monomers, cross-linking agents, etc. Adjusting the polymer concentration and dose of radiation, one can control the molecular weight and dimensions of nanogels. The products have been characterized by static light scattering, viscometry, and atomic force microscopy, while the nonclassical kinetics of intramolecular recombination has been followed by time-resolved spectroscopy. Nanogels of poly(acrylic acid) are much more resistant to free-radical-induced degradation than the parent linear chains.

Minimalism in Radiation Synthesis of Biomedical Functional Nanogels

“…Spectra were recorded at 30 scans per spectrum and 1 cm −1 resolution in the 4000−400 cm −1 range. 13 C { 1 H} CP-MAS NMR analysis was performed on solid samples with a Bruker Avance II 400 MHz (9.4 T) spectrometer operating at 400.15 MHz for the 1 H nucleus and 100.63 MHz for the 13 C nucleus with a MAS rate of 13 kHz, 1024 scans, a contact time of 1.5 ms and a repetition delay of 2 s. The optimization of the Hartmann−Hahn condition was obtained using an adamantane standard. All samples were placed in 4 mm zirconia rotors with KEL-F caps.…”

“…Solid-state 13 C NMR experimental data were provided by Centro Grandi Apparecchiature UniNetLab−Universitàdi Palermo, funded by P.O.R.Sicilia2000−2006, Misura 3.15 Quota Regionale.…”

Intramolecular Cross-Linking Methodologies for the Synthesis of Polymer Nanoparticles

“…One year later a detailed a study on radiationinduced intramolecular cross-linking of PAA and the properties of the nanogels formed was reported. 55 The authors discovered that the intramolecular cross-linking was preferred when many carbon-centered radicals were generated simultaneously along each PAA chain in dilute solutions. By changing the initial concentration of the polymer precursor and the dose absorbed by the sample, the average molecular weight and dimensions of these nanogels could be controlled (Scheme 2).…”

Preparation of Poly Acrylic Acid-Poly Acrylamide Composite Nanogels by Radiation Technique

“…These findings can be interpreted by the fact that intra-molecular recombination in dilute polymer solutions was established by low irradiation doses, while high doses were responsible for intermolecular cross-linking as well. 19 As F4 (fabricated with the highest weight ratio of PAAc to PAAm) showed the lowest size after irradiation with the 3 kGy dose among all formulations, it was selected for further studies (FTIR, SEM and MTT assay). SEM images of nanogels showed a good agreement with the obtained results from particle size analysis.…”